Die for the extrusion of heavy metals at high temperatures



March 18, 1969 G. NAESER ETAL 3,433,049

DIE FOR THE EXTRUSIQN OF HEAVY METALS AT HIGH TEMPERATURES Filed July 29, 1966 Fig] In venzors,

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762/; Adarnex United States Patent US. Cl. 72-467 4 Claims Int. Cl. B21c 3/00 ABSTRACT OF THE DISCLOSURE An extrusion die has a heat-resistant portion, a surface region of which, in contact with the metal block and with the product extruded therefrom, defines uniformly distributed fine pores, the porosity of which is from 10 to 50 percent.

The invention relates to the extrusion of metals and relates more particularly to extrusion dies for the extrusion of heavy metals at high temperatures.

During the forming of steel and other heavy metals into extruded products such as billets, tubes or other shapes by means of extrusion presses, there occurs considerable wear of the extrusion dies. This wear has proved to be a major expense.

Much labor and efl ort has, therefore, been spent to develop suitable materials for these extrusion dies, to increase the service life of extrusion dies, for instance by using special alloys. These developments were based on the thought to produce a hard and wear resistant steel for the die, that will withstand during the hot pressing the occurring changes in temperatures.

Attempts have furthermore been made to keep the surface temperature of the die as low as possible, either by the use of heat damming lubricants or by cooling of the die.

In accordance with another proposal (German Patent No. 560,186), it has been attempted to improve the durability of the dies by mounting hard metal carbides at those points of the die that are subjected to particularly strong wear; hard metal carbides of this type had proved valuable in cold drawing of metals. As these carbides cannot be melted, however, they may be produced only by powder metallurgy; they, therefore, retain a small residue of about 4% micropores. The quality of these materials decreases with increased amount of pores; for this reason the attempt has been made to keep the amount of pores at a minimum. (Kielfer-Schwarzkopf Hartstotfe und Hartmetall, Springer, Wien, 1953, pp. 433 and 448/449.)

As these pores had been regarded as detrimental, it has been proposed either to eliminate these microcavities or micropores by a polishing operation with the aid of draw nozzles that were composed of hard materials of the tungsten carbide family, or to close these micropores: by the grinding in of solid lubricants (German Patent No. 449,528).

Extrusion dies for the extrusion of steels and other heavy metals, which extrusion always takes place in glowing heat, normally today are made of molten metal that contains well-known suitable alloys, to increase the heat resistance of the dies. Heretofore, it has been thought to be particularly important that the material of the die be completely homogenous, and especially be free of pores, so as to avoid stresses and cracks in the dies during the temperature changes that occur during the extrusion operation, and at the same time to maintain the strength characteristics of the die material.

In contrast to the foregoing assumptions and thoughts which generally pervaded the field of experiences with hard metals, it has been found that the service life of the dies may be improved considerably if, in accordance with one of the principal objects of the invention, that portion of the die, the surface of which is adapted to be in contact with the metal block and with the product such as the billet extruded therefrom, includes at least a region near said surface which has a multitude of uniformly distributed fine pores.

It is another object of the invention to provide such a die at least the aforesaid region of which has through porosity.

It is a further object of the invention to provide that at least the aforesaid region may have a porosity of from about 10% to about 50%. Such a porosity inherently brings about a decrease in the heat conductivity of the material of that portion, which leads to an increase in the surface temperature of that portion. It has surprisingly, however, been found that nonetheless the durability and service life of such a die or aforesaid die portion is greater than that of dies as made heretofore of compact, completely homogenous material. In has, indeed, been shown that the expected chipping off fromvthe die at its exit end, where the die was made in accordance with the instant invention, did not take place.

Further objects and advantages of the invention will be set forth in part in the following specification and in part will be obvious therefrom without being specifically referred to, the same being realized and attained as pointed out in the claims hereof.

In accordance with a preferred embodiment of the instant invention, the instant porous dies or aforesaid die portions are produced in accordance with a well-known powder metallurgical method, namely from a steel powder which, for instance, may have been obtained by atomizing the liquid steel melt with pressure water; thereafter, either directly or following a soft annealing, the steel powder is pressed into suitable forms and sintered.

The instant invention provides that the well-known methods for improving the heat resistance of this material may be applied, such as dispersion hardening and/or embedding of most finely distributed non-metallic parts such as oxides or nitrides. It is also possible, in accordance with the invention, to produce the die pores which are disposed at least Within the aforesaid surface region, by means of other methods such as spark erosion or electrolytically, or by other similar methods.

The material for the extrusion dies, or for the aforesaid die portions or at least the aforesaid surface regions may have the following well-known alloy ingredients for high heat resistance, in the proportions set out below by way of example in percentages by weight:

Cobalt- Percent C 0.2 Si 0.5 Mn 2.3 Cr 18 to 20 Ni 11 W 15 Co 45 to 50 Nickel C .1 Cr 16 Mo 17 Ni 60 W 4 Fe 5 Iron C About .4 Cr 14 Ni 5 to 13 W 1.0 to 3.5 V About 1 Al About .5 Remainder Fe.

C Less than .1 Mn About 1.5 Cr About 18 Ni About Mo 2 to 5 Ti and/or Ta/Nb .2 to 1.0 Remainder Fe.

C Less than .1 Mn 1.0 to 1.5 Cr About 16 Ni 13 to 17 Mo About 2 Ti and/or Ta/Nb .2 to 1.0

Remainder Fe.

The heat resistance of the aforesaid exemplified alloys of which those under Nos. 1-4 have been used in practice, may be varied within limits, by the selection of the metal powder mixtures and the annealing operation. In this manner, there can be adjusted in a relatively simple way the contents of carbon, oxygen and nitrogen. As an alternative, for improving the heat resistance of the end product, it is possible to add carbides and oxides to the initial powder material; a particularly large heat resistance and thermosetting has been achieved with a nitrogen content of from about .5% to about 2.5% by weight in the aforesaid alloys.

Example Two or more metal powders which are produced by the nozzling of the melts, are so mixed in their percentages by weight that the total combination, for instance of the aforesaid nickel alloy, has about 60% by weight of nickel. The oxygen content and carbon content of the mixture are so chosen that there will be an excess of carbon of a desired magnitude, for instance about .1% C after the reaction of 2C+O =2CO. Thereafter, the powder mixture will be compacted in a steel die in a well-known manner to about 65% of the specific weight of the casting alloy. The unfinished pieces have the following dimensions:

Mm. Outside diameter 145 Inside diameter 95 Thickness 25 During the ensuing sintering at a rarefied pressure of 1 mm. Hg or less, for 10 hours at about 1200 0., there will take place simultaneously the deoxidation and decarburization in accordance with the preceding formula, and the specific weight will increase.

One tries to achieve thereby a pore volume of from about 10% to about 20%, which will be adjusted by subsequent pressing. By machining, the die or aforesaid die portion will be turned or ground on the outside, and a steel ring will be shrunk at a temperature of from 300 C. to 400 C. onto the die or die portion that has been produced with an allowance of about .3 mm.

If a high nitrogen content is desired, this can be achieved simply by filling the vacuum furnace with nitrogen during the cooling at a temperature of about 950 C.

To provide a die or die portion with a porous surface may be achieved in accordance with a wellknown method and machine by spark erosion. The workpiece is connected to the positive anode, and the tool to the negative electrode. The tool may, for instance, be a brush with bristles made of copper or brass, the form of which corresponds to the inner diameter of the die or die portion, and the width of which at any one time works approximately at a one-half quadrant. The holes made in accordance with this procedure have a diameter of less than .5 mm. and a depth of from .5 to 1 mm. The distance between the holes is as small as possible, that means less than 1 mm.

In the accompanying drawings:

FIG. 1 is a vertical sectional view of a die including a die portion in accordance with an embodiment of the invention;

FIG. 2 is a sectional view, similar to FIG. 1, but embodying a modification;

FIG. 3 is a sectional view, similar to FIG. 1, but embodying a further modification; and

FIG. 4 is a sectional view, similar to FIG. 1, showing another modification.

In FIG. 1, there is shown a die including a die portion 1. The die portion 1 has been produced metallurgically and is surrounded by a steel ring 2 that is shrunk onto the portion 1. As the portion 1, due to its porosity, has only a small tensile strength, it should be under compressive stress due to the steel ring 2 shrunk thereonto, so that during the extrusion the tensile stress occurring on the inner surface of the portion 1 will be as small as possible, preferably zero.

The modification of FIG. 2 is similar to the embodiment of FIG. 1, but the portion 1 has a conically outward flaring outlet 3.

FIG. 3 shows a die that has a compact base 2 that carries a porous layer 4, 5 of the aforesaid material that constitutes a surface region near the surface; the surface extends throughout an area in which it makes contact with the metal block, as well as with the extruded product. The porosity of the layer 5 may, for instance, have been produced by spark erosion.

The die of FIG. 4 is similar to that of FIG. 3, but shows the conical flaring out 3 of FIG. 2. The porous layer 5 inside the die terminates in advance of the edge of the outlet 3. The porous layer 4 near the upper surface of the die that faces the extrusion press and the metal block does not, as shown in FIG. 3, need to extend to the border of the die, because the edge portion near the border of the die is in a so-called dead zone in which there is no contact with the metal block.

We wish it to be understood that we do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

Having thus described the invention, what we claim as new and desire to be secured by Letters Patent, is as follows:

1. An extrusion die, for use in connection with an extrusion press for the extrusion at high temperatures of a metal block, said die including a portion composed of a highly heat resistant metal alloy including cobalt, nickel and iron and comprising a surface region extending at least throughout an area in which the surface thereof is adapted to be in contact with the metal block and wrth the product extruded therefrom, at least said surface region of said portion defining uniformly distributed fine pores, the porosity being from 10 percent to 50 percent.

2. A die, as claimed in claim 1, at least said region having through porosity,

3. A die, as claimed in claim 1, said portion being composed of powdered material.

4. A die, as claimed in claim 1, and a steel ring surrounding and being shrunk onto said portion.

References Cited UNITED STATES PATENTS 2,027,737 1/1936 Ridgway 6t a1. 72-467 2,753,261 7/1956 Goetzel et al 72 467 X 3,222,902 12/1965 Brejcha et a1 72 56 l0 MILTON S. MEHR, Primary Examiner.

US. Cl. X.R. 

